The lack of functional expression of proteins at the cell surface due to misfolding has been linked to number of genetic diseases, including familial hypercholesterolemia and cystic fibrosis. However, the molecular mechanisms responsible for correct folding of membrane proteins in the ER remain poorly understood. The goal of the proposed studies is to investigate the molecular mechanisms of folding and surface expression of CFTR, a polytopic integral membrane protein. Experiments outlined in the first aim will focus on identification of proteins involved in CFTR folding/surface expression. For this purpose a genetic screen will be carried out in mammalian cells to identify high copy extra genic suppressors of deltaF508 CFTR processing defect. Isolation of CFTR folding modulators and characterization of their interactions with both the wild type and mutant CFTR should provide insights into the cellular regulation of CFTR surface expression. The second aim is to identify second-site mutations within deltaF508 CFTR molecule that can restore its proper folding and surface expression. These experiments will utilize PCR-based mutagenesis combined with expression cloning in mammalian cells. Understanding of membrane protein folding mechanisms is central for issues of cell biology and new insights into the regulation of CFTR folding and surface expression can be instrumental in the development of treatments for genetic diseases caused by protein folding/trafficking defects.